1. Field of the Invention
A miniature fuse receivable in a miniature socket that is series-connected in a decorative string of miniature sockets that contain miniature incandescent lamps.
2. Description of the Prior Art
Heretofore, strings of miniature decorative incandescent lamps have constituted a large number of miniature sockets, for example, thirty-four sockets, each of which had a miniature such lamp press-fitted therein. This arrangement enabled both the sockets and the lamps to be of very simple design and of small size and low cost. The sockets, and therefore the lamps, were connected in series, and the lamps often were so constructed that if one of them blew out, an alternate, i.e. shunt path, was supplied for the current so that the string, as a whole, would continue to function. However, the shunt path was so designed that when the associated lamp filament burned out, the current flowing through the shunt was greater than the current that previously flowed through the shunt when it was connected in parallel with the filament.
Therefore, after a lamp blew out, the flow of current through the string increased. If such increase were permitted to rise above a predetermined current flow, the string would heat up and could ignite some adjacent object. The entire string could be damaged by the heat build-up. The remaining lamps would glow brighter, thereby reducing their working lifetimes. The wires could melt if the current was high enough, and the resulting heat could cause a fire and damage objects in one's home. Therefore, it was customary to include two fuses, one at each end of the string, and each fuse was connected in series.
Usually, the fuses used heretofore were designed to be press-fitted into miniature sockets. These fuses, as a rule, took the form of miniature incandescent lamps that were unshunted and the filaments of which were designed to burn out when the series current flowing through the string rose to too high a value thereby causing the unshunted filaments to act as fuses.
These prior fuses were designed to carry a heavier load than the balance of the miniature lamps inasmuch as they had to be prepared to assimilate and radiate the heat consequent upon the blowing of a few of the miniature lamps and the consequent increase in the series current. Likewise, the miniature sockets for these lamps were made heavier than the miniature sockets for the miniature lamps of the remaining components of the string. Hence, two different kinds of sockets had to be used with increase in the cost for making the socket and with increase in the cost for assembling the sockets in the string due to the necessity of maintaining the heavier and lighter sockets separate from one another and incorporating them at different points of the string, the fuse sockets being at the ends of the string.
These lamps, i.e. lamps which act as fuses, are shown in U.S. Pat. No. 4,030,059, although fuse lamps for Christmas trees date back more than a decade before that patent. The use of unshunted fuse lamps in combination with shunted miniature lamps is the subject of U.S. Pat. No. 3,968,398, although this combination likewise was sold more than a decade before that patent.
Other patents more remotely related to the present invention include U.S. Pat. Nos. 2,831,087; 3,110,787; and 4,080,039.